In vitro fertilization (IVF) provides infertile couples hope of conceiving in spite of a wide variety of causes for the infertility. The success rates of IVF have continued to rise, accompanied, unfortunately, by a large increase in the risk of multiple pregnancy.
Current protocols include two strategies for minimizing the risk of multiple pregnancy while maximizing the chance of a successful cycle (pregnancy). Established IVF protocols generally include embryo transfer on the third day after fertilization (culture day 3, or CD 3). The best embryos are identified by morphologic criteria, symmetry between the blastomeres, number of blastomeres, and evidence of degeneration of the blastomeres. Unfortunately, morphologic criteria on CD 3 are poorly predictive of the chance of establishing pregnancy. See, e.g., Milki et al (2002) Fertil Steril 77, 1191-5; and Rijnders et al. (1998) Hum Reprod 13, 2869-73. The number of embryos transferred varies from 1 to 4, based on guidelines published by the American Society for Reproductive Medicine. These guidelines use criteria based on the age of the patient, number of previous successful or unsuccessful attempts, and the quality as assessed by morphologic criteria. Unfortunately this can result in implantation of up to four embryos and high order multiple pregnancy. Another strategy for combating the risk of multiple pregnancy is extended embryo culture in which the embryos are held in culture for five days after oocyte retrieval. The development and commercial availability of sequential embryonic media has made extended embryo culture a potentially useful tool to improve assisted reproductive technologies (ART) efficiency and further reduce multiple births. Papanikolaou et al. N Engl J Med 354, 1139-46, in a prospective randomized controlled trial of women under 36 years of age, compared ET of a single cleavage stage embryo (CD 3) with a single blastocyst (CD 5 embryo) and reported a significantly higher rate of pregnancy and delivery in the blastocyst group. The transfer of fewer embryos at the blastocyst stage has the potential to reduce multiple births without compromising the overall pregnancy rate.
One of the major disadvantages of extended culture, however, has been the worry that in approximately 40% of patients, no embryos would be available for transfer in a given cycle. Proponents of extended culture believe that refractory embryos would not be developmentally competent in utero; however, justification for this is lacking and failure to proceed to embryo transfer (ET) subsequent to controlled ovarian hyperstimulation (COH) can have obvious emotional and financial implications. In addition, the possibility of an increased incidence of imprinting errors (Beckwith-Weideman syndrome, Angelman syndrome) associated with IVF raises concerns about universal use of extended embryo culture.
Day 5 transfer has the potential for maximizing pregnancy rate but minimizing the multiple pregnancy rate. Day 3 transfer is more cost effective and minimizes the chance that there will be no embryo to transfer. It is apparent that the ability to predict embryonic progression at an earlier stage could potentially influence decisions regarding embryo culture protocols and ET day. There is a need for a quantifiable objective measure of embryonic health, preferably one that reflects metabolic function, which can be used to predict at an early time post insemination/injection if an embryo exhibits high quality and will progress to at least the blastocyst stage.